linux-kernel - Re: [PATCH v2] x86/nmi: Add an emergency handler in nmi_desc & use it in nmi_shootdown

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Message-ID: <87zflbqqar.ffs@tglx>
Date: Wed, 04 Dec 2024 19:03:08 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: Waiman Long <llong@...hat.com>, Ingo Molnar <mingo@...hat.com>, Borislav
 Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, Peter
 Zijlstra <peterz@...radead.org>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, "H. Peter Anvin"
 <hpa@...or.com>
Subject: Re: [PATCH v2] x86/nmi: Add an emergency handler in nmi_desc & use
 it in nmi_shootdown_cpus()

On Wed, Dec 04 2024 at 12:23, Waiman Long wrote:
> On 12/4/24 8:10 AM, Thomas Gleixner wrote:
>> On Tue, Dec 03 2024 at 10:07, Waiman Long wrote:
>>> +	/*
>>> +	 * Call the emergency handler first, if set
>>> +	 * Emergency handler is not traced or checked by nmi_check_duration().
>>> +	 */
>>> +	ehandler = READ_ONCE(desc->emerg_handler);
>>> +	if (ehandler)
>>> +		handled = ehandler(type, regs);
>> Shouldn't this just stop processing right here?
>
> Yes in the case of crash_nmi_callback(). I suppose it is a no-return 
> call. As the emergency handler is supposed to be a general mechanism in 
> design, I don't want to make too many assumptions of what will happen 
> when the handler is invoked.

I'm not convinced that this should be used as a general mechanism. It's
for emergency situations and that's where it stops. If the thing
returns, it's a bug IMO.

Thanks,

        tglx